Anti-cooperative oxidation of ubiquinol by the yeast cytochrome bc1 complex
Anti-cooperative oxidation of ubiquinol by the yeast cytochrome bc1 complex
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DOI：
10.1074/jbc.m400193200
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发表时间：
2004-04-09
影响因子：
4.8
通讯作者：
Trumpower, BL
中科院分区：
文献类型：
--
作者：
Covian, R;Gutierrez-Cirlos, EB;Trumpower, BL
我们研究了二聚体酵母细胞色素bc（1）复合物的单体之间的相互作用，通过分析分离的酶在抗霉素存在下的前稳态和稳态活性，在允许泛醇氧化的第一个营业额的条件下，可以观察到细胞色素c（1）还原。在pH8.8时，铁硫蛋白的氧化还原电位与200 mV相似，在bc（1）复合物中，突变的铁硫蛋白的氧化还原电位同样低，在抗霉素存在下，几当量的癸基泛醇还原的细胞色素c（1）的量仅相当于bc（1）复合物中存在的量的一半。在几个当量的细胞色素c存在下的类似实验也显示只有一半的bc（1）复合物参与了对苯二酚的氧化。细胞色素B的还原程度对应于两个B（H）血红素通过每个二聚体的一个中心P进行还原，表明两个细胞色素B亚基之间的电子转移。在低抑制剂/酶比下，抗霉素刺激bc（1）复合物的泛喹啉-细胞色素c还原酶活性。这种刺激只能适用于这样一种模型，即当两个中心N位点都自由时，bc（1）二聚体的一半是无活性的，当每个二聚体结合一个中心N抑制剂分子时变得有活性，并且二聚体的细胞色素B亚基之间存在电子转移。这些结果与bc（1）复合物二聚体中泛醇氧化的交替半位点机制一致。
We have investigated the interaction between monomers of the dimeric yeast cytochrome bc(1) complex by analyzing the pre-steady and steady state activities of the isolated enzyme in the presence of antimycin under conditions that allow the first turnover of ubiquinol oxidation to be observable in cytochrome c(1) reduction. At pH 8.8, where the redox potential of the iron-sulfur protein is similar to 200 mV and in a bc(1) complex with a mutated iron-sulfur protein of equally low redox potential, the amount of cytochrome c(1) reduced by several equivalents of decyl-ubiquinol in the presence of antimycin corresponded to only half of that present in the bc(1) complex. Similar experiments in the presence of several equivalents of cytochrome c also showed only half of the bc(1) complex participating in quinol oxidation. The extent of cytochrome b reduced corresponded to two b(H) hemes undergoing reduction through one center P per dimer, indicating electron transfer between the two cytochrome b subunits. Antimycin stimulated the ubiquinol-cytochrome c reductase activity of the bc(1) complex at low inhibitor/enzyme ratios. This stimulation could only be fitted to a model in which half of the bc(1) dimer is inactive when both center N sites are free, becoming active upon binding of one center N inhibitor molecule per dimer, and there is electron transfer between the cytochrome b subunits of the dimer. These results are consistent with an alternating half-of-the-sites mechanism of ubiquinol oxidation in the bc(1) complex dimer.